If you really want a serum, Korres makes one in their anti-aging/anti-wrinkle formulation for all skin types. They also have a new pomegranate line that has a treatment in there to really control oil, as well as a moisturizer! You should go into your local Sephora and get you a sample or two!
Answered[ Edited ]
My two favorite serums are Ole Henrikson's Truth Serum and Josie Maran Argan Oil (not exactly a serum, but similar). They are not for oily skin but they do not make it any oilier either. Only use a drop or two.
I am adding Bare Escentuals Active Cell Renewal Night Serum. It's a new formula and I have never used it, but it has ActiveSoil Complex which speeds up cell turnover and in some of their other products it has helped my acne.